It has been known for a long time that UV radiation has a germicidal effect and that the naturally occurring UV radiation in sunlight has a disinfecting effect at sufficient intensity and duration. UV radiation is used in small and large facilities for the disinfection of water and waste water. It is possible to distinguish between facilities in which UV emitters are arranged in closed channels and facilities in which the UV emitters are in channels which are open at the top, known as open channels. The second type of construction with open channels is primarily used in waste water technology. The purified waste water is guided through an open channel into the UV system and exposed to UV radiation in order to reduce the number of germs to a level such that the purified waste water can, for example, be discharged into normal waters. The level of disinfection can be so high as to allow the water to be discharged into bathing water.
Waste water treatment facilities are normally designed so that the water flows from an inlet through the various different treatment levels to an outlet solely by the force of gravity, without the need for any pumps. For this reason, in UV treatment systems in waste water technology too, the aim is to keep the flow resistance as low as possible in order to achieve as low a loss in pressure as possible from the intended throughflow rate. In the operation of the facility, a loss of pressure of this type would manifest itself as a height difference between the water level in the inlet and the water level in the outlet. The aim is to keep this height difference as low as possible.
Otherwise, the disinfection capacity of the system must be ensured, with the level of effectiveness of the system being expressed in the ratio between disinfection achieved and electrical power used. This level of effectiveness should be optimised for economic reasons. For this reason, UV emitters, which are generally elongated gas discharge lamps, are placed in the channel, preferably in rows transverse to the flow. Several rows are arranged one after the other and offset against one another such that the emitters in one row are arranged in the centre between the emitters in the row arranged upstream. The water that flows between the first emitters will then hit the subsequent emitter which is in the centre behind the gap. This arrangement results in different spaces between the emitters in the different rows and the lateral, adjacent wall of the channel. In areas in which there is a large gap between the emitter and the wall of the channel, the dose of radiation is lower than in the other areas. This effect should be compensated for in order that every flow pathway which can occur in practice receives a sufficient and, where possible, equal dose of UV.
Various different solutions for this are known from the prior art. Essentially, the known solutions are based on continuous, beam-shaped elements with various different cross sections being arranged on the wall of the channel which reduce the space between the adjacent UV emitter and the wall of the channel, thereby narrowing the gap there. Document . . . for example shows a channel with four rows each of four UV emitters which are arranged one after the other in the flow direction and the flow passes by them transverse to their longitudinal axis. In the open channel, the emitters therefore hang vertically. A rib with a triangular cross section is arranged next to the emitter which is the farthest from the wall, which rib narrows the cross section of the gap between the wall and the emitter through which water can flow freely. Document WO 2008055344 A1, which is incorporated by reference herein, shows various different solutions which also work with ribs with a triangular cross section, whereby the ribs on the one hand narrow the free cross section and on the other deflect the flow.
Document EP 0893411 B1, which is incorporated by reference herein, shows a solution in which an L-shaped profile is arranged laterally on the wall of the channel and here, with the rows of UV emitters arranged behind one another and offset against one another in the area where the UV emitter closest to the edge is farthest away from the wall of the channel. The L-profile is arranged continuously along the entire length of the adjacent emitter on the wall. It deflects the water flow in this area essentially completely. The aim here is to divert the flow of the water in the edge area completely to the emitter arranged at a distance from the wall.
The technical solutions described therefore aim to impact the flow pathways of the water or waste water flowing through the channel such that in the area in which the radiation intensity is higher they also reach the areas where the emitter is at a greater distance from the adjacent wall of the channel. In practice, this results in two problems. On the one hand, the complete deflection of the flow pathways by the installations which extend with the same shaped cross section over the entire length of the adjacent emitter along the wall of the channel significantly narrows the free cross section of the channel, so the loss in pressure between the upstream side of the channel system and the downstream side of the channel system increases. On the other hand, the flow is accelerated in the region of these installations, so the flow pathways are deflected in the region in which there is higher intensity, but the length of time spent in this area is shorter. The goal of increasing the dose of UV applies to the flow pathway is not optimally achieved in this way.